A motor drive mechanism is detachably mounted on a camera, or it is incorporated in the camera body to carry out an automatic winding operation of film in the camera. The release operation of the camera shutter is generally carried out in accordance with the following three methods in cameras using motorized winding mechanisms:
(a) The locking is purely mechanically released by the force of depressing the release button, thereby to effect the release operation;
(b) The motor is used for the winding operation only. The release operation is effectuated by an exciting magnet or solenoid which is operated upon energization;
(c) The winding and release operations are carried out by one motor. By utilizing the effect of increased resistance to winding abruptly before the completion of the operation, the motor is disconnected from the winding mechanism, connected to the release mechanism, and the release operation is carried out by the force of the motor.
In the first method, the motor drive mechanism can be considerably simplified, because in principle the winding operation is effectuated through a reduction gear mechanism (such as a gear train) by the output shaft of the motor and the operation of the motor. The motor is controlled by a switch which is operated in association with a member which turns through a predetermined angle during one winding operation in the camera. In this method, the force of the motor is not needed for the release operation. However, in the first method, the release operation cannot be electrically carried out, and therefore this method is not suitable for continuous or remote photographing. Rather it is suitable for low-grade cameras which can be manufactured at relatively low cost.
In the second method, as in the first, the motor is used for the winding operation only, and an exciting magnetic or solenoid latch is used for the release operation. The relationship between the winding operation and the release operation can be electrically isolated, for instance, in such a manner that the release operation will not be carried out during the winding operation. Therefore, the construction of the motor drive mechanism according to the second method can be simplified. Unlike the first method in the second the release operation can be effected electrically, and therefore realization of high-grade motor drive operations such as continuous and remote photographing can be attained. The disadvantages are although a type of rotating solenoid in the form of an electric motor is incorporated and the rotation of the motor can be utilized for the release operation, since the winding operation is completed before the release operation, it is necessary to provide an additional solenoid for the release operation. This contributes to an increase in manufacturing cost. Also, since an exciting magnet or solenoid which is, in principle, unsuitable for providing strong force over a long stroke is employed for releasing the locking mechanism, it is necessary to form a locking section which can release the locking mechanism with a force and a stroke which are less than those in the case of the conventional locking section. Therefore, the motor drive mechanism according to the second method is affected by shock and by components interposed between the solenoid or the like and the locking section. Accordingly, it is absolutely necessary to incorporate the additional solenoid in the camera. This limitation inhibits the degree of freedom of the camera designer in configuring the construction of the product.
The third method is the orthodox technique for a motor drive mechanism. As is well known in the art, many types of motor drive mechanisms have been proposed in accordance with this method. Since the release operation can be effected electrically, a highgrade motor drive operation can be realized similarly as in the first method. In this technique, the output of the motor rotation in one direction is switched upon completion of the winding operation so that it is used for the release operation instead of the winding operation. The variation of the force necessary for winding is used as a switching signal, and the clutch is switched with the aid of the force of the motor. Therefore, the third method is disadvantageous in that the clutch section is rather intricate and the switching mechanism is also complicated. The fundamental object of the third method is to operate a camera which has a traditional mechanism without a motor drive system, with an added motor drive module. Since the release operation is effected by the motor, a releasing force greater than that in the motor drive mechanism according to the third method is configured in such a manner that it can be detachably mounted on a camera.